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  线程安全进阶
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  <h1 id="线程安全"><a href="#线程安全" class="headerlink" title="线程安全"></a>线程安全</h1><p><a target="_blank" rel="noopener" href="https://blog.csdn.net/mulinsen77/article/details/84583716">https://blog.csdn.net/mulinsen77/article/details/84583716</a></p>
<h2 id="AbstractQueuedSynchronizer-类"><a href="#AbstractQueuedSynchronizer-类" class="headerlink" title="AbstractQueuedSynchronizer 类"></a>AbstractQueuedSynchronizer 类</h2><p>又名 AQS 框架，位于 java.util.concurrent.locks 包内。用来构建锁和同步器的框架，使用 AQS 能简单且高效地构造出应用广泛的大量的同步器，比如我们提到的 ReentrantLock，Semaphore 等。</p>
<p>AQS 核心思想是通过以下方式，建立一套线程阻塞等待以及被唤醒时锁分配的机制。</p>
<ul>
<li>如果被请求的共享资源空闲，则将当前请求资源的线程设置为有效的工作线程，并且将共享资源设置为锁定状态。</li>
<li>如果被请求的共享资源被占用，就将暂时获取不到锁的线程封装成一个结点，加入到一个虚拟的双向队列 CLH 中。</li>
</ul>
<p><em>CLH 不存在真实的队列，仅存在结点之间的关联关系。</em></p>
<p><img src="/pic/CLH.png" alt="CLH"></p>
<h3 id="AQS-存储状态"><a href="#AQS-存储状态" class="headerlink" title="AQS 存储状态"></a>AQS 存储状态</h3><p>AQS 负责维护：</p>
<ol>
<li>一个 volatile int 成员变量 state</li>
<li>一个 FIFO 线程等待队列</li>
</ol>
<p>成员变量 state 表示资源状态，通过 getState/setState 方法存取。</p>
<p>线程抢占资源时会通过 CAS 操作去尝试修改 state ，成功则获取锁成功，失败则进入等待队列等待被唤醒。</p>
<h3 id="资源共享方式"><a href="#资源共享方式" class="headerlink" title="资源共享方式"></a>资源共享方式</h3><p>AQS 定义两种资源共享方式</p>
<ul>
<li><strong>Exclusive（独占）</strong></li>
</ul>
<p>只有一个线程能执行，如 ReentrantLock。</p>
<p>state初始化为0，表示未锁定状态。加一后锁定。</p>
<ul>
<li><strong>Share（共享）</strong></li>
</ul>
<p>多个线程可同时执行，如 Semaphore/CountDownLatch。Semaphore、CountDownLatCh、 CyclicBarrier、ReadWriteLock 。</p>
<p>返回 state 负数表示失败；0表示成功，但没有剩余可用资源；正数表示成功，且有剩余资源。</p>
<h3 id="自定义同步器"><a href="#自定义同步器" class="headerlink" title="自定义同步器"></a>自定义同步器</h3><p>同步器的设计是基于模板方法模式的，如果需要自定义同步器一般的方式是这样（模板方法模式很经典的一个应用）：</p>
<p>同步类在实现时一般都将自定义同步器（sync）定义为内部类，供自己使用；而同步类自己（Mutex）则实现某个接口，对外服务。</p>
<p>使用者继承 AbstractQueuedSynchronizer 并重写指定的方法。（这些重写方法很简单，无非是对于共享资源 state 的获取和释放）<br>将 AQS 组合在自定义同步组件的实现中，并调用其模板方法，而这些模板方法会调用使用者重写的方法。</p>
<p>isHeldExclusively()：该线程是否正在独占资源。只有用到condition才需要去实现它。<br>tryAcquire(int)：独占方式。尝试获取资源，成功则返回true，失败则返回false。<br>tryRelease(int)：独占方式。尝试释放资源，成功则返回true，失败则返回false。<br>tryAcquireShared(int)：共享方式。尝试获取资源。负数表示失败；0表示成功，但没有剩余可用资源；正数表示成功，且有剩余资源。<br>tryReleaseShared(int)：共享方式。尝试释放资源，如果释放后允许唤醒后续等待结点返回true，否则返回false。</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">class</span> <span class="title class_">Mutex</span> <span class="keyword">implements</span> <span class="title class_">Lock</span>, java.io.Serializable &#123;</span><br><span class="line">    <span class="comment">// 自定义同步器</span></span><br><span class="line">    <span class="keyword">private</span> <span class="keyword">static</span> <span class="keyword">class</span> <span class="title class_">Sync</span> <span class="keyword">extends</span> <span class="title class_">AbstractQueuedSynchronizer</span> &#123;</span><br><span class="line">        <span class="comment">// 判断是否锁定状态</span></span><br><span class="line">        <span class="keyword">protected</span> <span class="type">boolean</span> <span class="title function_">isHeldExclusively</span><span class="params">()</span> &#123;</span><br><span class="line">            <span class="keyword">return</span> getState() == <span class="number">1</span>;</span><br><span class="line">        &#125;</span><br><span class="line"></span><br><span class="line">        <span class="comment">// 尝试获取资源，立即返回。成功则返回true，否则false。</span></span><br><span class="line">        <span class="keyword">public</span> <span class="type">boolean</span> <span class="title function_">tryAcquire</span><span class="params">(<span class="type">int</span> acquires)</span> &#123;</span><br><span class="line">            <span class="keyword">assert</span> acquires == <span class="number">1</span>; <span class="comment">// 这里限定只能为1个量</span></span><br><span class="line">            <span class="keyword">if</span> (compareAndSetState(<span class="number">0</span>, <span class="number">1</span>)) &#123;<span class="comment">//state为0才设置为1，不可重入！</span></span><br><span class="line">                setExclusiveOwnerThread(Thread.currentThread());<span class="comment">//设置为当前线程独占资源</span></span><br><span class="line">                <span class="keyword">return</span> <span class="literal">true</span>;</span><br><span class="line">            &#125;</span><br><span class="line">            <span class="keyword">return</span> <span class="literal">false</span>;</span><br><span class="line">        &#125;</span><br><span class="line"></span><br><span class="line">        <span class="comment">// 尝试释放资源，立即返回。成功则为true，否则false。</span></span><br><span class="line">        <span class="keyword">protected</span> <span class="type">boolean</span> <span class="title function_">tryRelease</span><span class="params">(<span class="type">int</span> releases)</span> &#123;</span><br><span class="line">            <span class="keyword">assert</span> releases == <span class="number">1</span>; <span class="comment">// 限定为1个量</span></span><br><span class="line">            <span class="keyword">if</span> (getState() == <span class="number">0</span>)<span class="comment">//既然来释放，那肯定就是已占有状态了。只是为了保险，多层判断！</span></span><br><span class="line">                <span class="keyword">throw</span> <span class="keyword">new</span> <span class="title class_">IllegalMonitorStateException</span>();</span><br><span class="line">            setExclusiveOwnerThread(<span class="literal">null</span>);</span><br><span class="line">            setState(<span class="number">0</span>);<span class="comment">//释放资源，放弃占有状态</span></span><br><span class="line">            <span class="keyword">return</span> <span class="literal">true</span>;</span><br><span class="line">        &#125;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="comment">// 真正同步类的实现都依赖继承于AQS的自定义同步器！</span></span><br><span class="line">    <span class="keyword">private</span> <span class="keyword">final</span> <span class="type">Sync</span> <span class="variable">sync</span> <span class="operator">=</span> <span class="keyword">new</span> <span class="title class_">Sync</span>();</span><br><span class="line"></span><br><span class="line">    <span class="comment">//lock&lt;--&gt;acquire。两者语义一样：获取资源，即便等待，直到成功才返回。</span></span><br><span class="line">    <span class="keyword">public</span> <span class="keyword">void</span> <span class="title function_">lock</span><span class="params">()</span> &#123;</span><br><span class="line">        sync.acquire(<span class="number">1</span>);</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="comment">//tryLock&lt;--&gt;tryAcquire。两者语义一样：尝试获取资源，要求立即返回。成功则为true，失败则为false。</span></span><br><span class="line">    <span class="keyword">public</span> <span class="type">boolean</span> <span class="title function_">tryLock</span><span class="params">()</span> &#123;</span><br><span class="line">        <span class="keyword">return</span> sync.tryAcquire(<span class="number">1</span>);</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="comment">//unlock&lt;--&gt;release。两者语文一样：释放资源。</span></span><br><span class="line">    <span class="keyword">public</span> <span class="keyword">void</span> <span class="title function_">unlock</span><span class="params">()</span> &#123;</span><br><span class="line">        sync.release(<span class="number">1</span>);</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="comment">//锁是否占有状态</span></span><br><span class="line">    <span class="keyword">public</span> <span class="type">boolean</span> <span class="title function_">isLocked</span><span class="params">()</span> &#123;</span><br><span class="line">        <span class="keyword">return</span> sync.isHeldExclusively();</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<hr>
<h2 id="ReentrantReadWriteLock-锁"><a href="#ReentrantReadWriteLock-锁" class="headerlink" title="ReentrantReadWriteLock 锁"></a>ReentrantReadWriteLock 锁</h2><p>Java 的并发包提供了读写锁 ReentrantReadWriteLock ，其拥有两个锁：读锁-共享锁；写锁-排他锁。如果其他线程没有持有写锁，线程就能获得读锁。而只有其他线程没有持有任何锁，线程才能获得写锁。这样在没有写操作的时候，允许多个线程同时读一个资源，提高并发效率。</p>
<p>一个线程要想同时持有写锁和读锁，必须先获取写锁再获取读锁；写锁可以降级为读锁；读锁不能升级为写锁。</p>
<h2 id="Semaphore-信号量"><a href="#Semaphore-信号量" class="headerlink" title="Semaphore 信号量"></a>Semaphore 信号量</h2><p>Semaphore 类是一个同步工具类，需要进行导入：<code>import java.util.concurrent.Semaphore</code>。</p>
<p>synchronized 和 ReentrantLock 一次只允许一个线程访问某个资源，如果指定多个线程同时访问某个资源需要钱使用 Semaphore 类。线程执行时调用 acquire 方法申请信号量，如果剩余信号量不足则必须等待其他线程执行完毕后调用 release 方法释放信号量。</p>
<p><strong>Semaphore 方法</strong></p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br></pre></td><td class="code"><pre><span class="line"><span class="type">Semaphore</span> <span class="variable">semaphore</span> <span class="operator">=</span> <span class="keyword">new</span> <span class="title class_">Semaphore</span>(<span class="number">0</span>);       </span><br><span class="line"><span class="type">Semaphore</span> <span class="variable">semaphore</span> <span class="operator">=</span> <span class="keyword">new</span> <span class="title class_">Semaphore</span>(<span class="number">20</span>, <span class="literal">true</span>);  </span><br><span class="line"></span><br><span class="line"><span class="comment">// Semaphore 构造方法设定了初始信号量，可以为 0。默认为非公平锁，设定属性 true 则为公平锁。</span></span><br><span class="line"></span><br><span class="line">semaphore.acquire();              <span class="comment">// 线程获取一个信号量</span></span><br><span class="line">semaphore.acquire(<span class="number">5</span>);             <span class="comment">// 线程获取五个信号量</span></span><br><span class="line"></span><br><span class="line">semaphore.release();              <span class="comment">// 线程释放一个信号量</span></span><br><span class="line">semaphore.release(<span class="number">5</span>);             <span class="comment">// 线程释放五个信号量</span></span><br><span class="line"></span><br><span class="line">semaphore.availablePermits();     <span class="comment">// 读取剩余信号量</span></span><br></pre></td></tr></table></figure>

<p><strong>Semaphore 示例</strong></p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="keyword">class</span> <span class="title class_">SemaphoreExample1</span> &#123;</span><br><span class="line"></span><br><span class="line">  <span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title function_">main</span><span class="params">(String[] args)</span> <span class="keyword">throws</span> InterruptedException &#123;</span><br><span class="line">    <span class="type">ExecutorService</span> <span class="variable">threadPool</span> <span class="operator">=</span> Executors.newFixedThreadPool(<span class="number">300</span>);</span><br><span class="line">    <span class="comment">// 设置 20 个信号量</span></span><br><span class="line">    <span class="keyword">final</span> <span class="type">Semaphore</span> <span class="variable">semaphore</span> <span class="operator">=</span> <span class="keyword">new</span> <span class="title class_">Semaphore</span>(<span class="number">20</span>);</span><br><span class="line">    <span class="comment">// final Semaphore semaphore = new Semaphore(20, true);  公平锁</span></span><br><span class="line"></span><br><span class="line">    <span class="keyword">for</span> (<span class="type">int</span> <span class="variable">i</span> <span class="operator">=</span> <span class="number">0</span>; i &lt; <span class="number">500</span>; i++) &#123;</span><br><span class="line">      <span class="keyword">final</span> <span class="type">int</span> <span class="variable">threadnum</span> <span class="operator">=</span> i;</span><br><span class="line">      threadPool.execute(() -&gt; &#123;</span><br><span class="line">        <span class="keyword">try</span> &#123;</span><br><span class="line">          semaphore.acquire();             <span class="comment">// 获取一个信号量</span></span><br><span class="line">          test(threadnum);</span><br><span class="line">          semaphore.release();             <span class="comment">// 释放一个信号量</span></span><br><span class="line">        &#125; <span class="keyword">catch</span> (InterruptedException e) &#123;</span><br><span class="line">          e.printStackTrace();</span><br><span class="line">        &#125;</span><br><span class="line"></span><br><span class="line">      &#125;);</span><br><span class="line">    &#125;</span><br><span class="line">    threadPool.shutdown();</span><br><span class="line">    System.out.println(<span class="string">&quot;finish&quot;</span>);</span><br><span class="line">  &#125;</span><br><span class="line"></span><br><span class="line">  <span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title function_">test</span><span class="params">(<span class="type">int</span> threadnum)</span> <span class="keyword">throws</span> InterruptedException &#123;</span><br><span class="line">    Thread.sleep(<span class="number">1000</span>);</span><br><span class="line">    System.out.println(<span class="string">&quot;threadnum:&quot;</span> + threadnum);</span><br><span class="line">    Thread.sleep(<span class="number">1000</span>);</span><br><span class="line">  &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<hr>
<h2 id="CountDownLatch-倒计时器"><a href="#CountDownLatch-倒计时器" class="headerlink" title="CountDownLatch 倒计时器"></a>CountDownLatch 倒计时器</h2><p>CountDownLatch 类是一个同步工具类，需要进行导入：<code>import java.util.concurrent.CountDownLatch</code>。</p>
<p>其通过 await 方法设置一个屏障，线程到达后被阻塞。直到其他线程调用 countDown 方法达到 N 次后才允许向后执行。 CountDownLatch 类是一次性的，计数器值只能在构造方法中初始化一次，不能被重复使用。常用来协同多个线程之间的执行顺序，比如主线程需要等待多个组件加载完毕之后再继续执行。</p>
<p><strong>CountDownLatch 方法</strong></p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line"><span class="type">CountDownLatch</span> <span class="variable">latch</span> <span class="operator">=</span> <span class="keyword">new</span> <span class="title class_">CountDownLatch</span>(<span class="number">5</span>);</span><br><span class="line"></span><br><span class="line"><span class="comment">// CountDownLatch 构造方法设定了门闩个数。</span></span><br><span class="line"></span><br><span class="line">latch.countDown();                <span class="comment">// 解锁门闩，门闩个数减一</span></span><br><span class="line">latch.await();                    <span class="comment">// 线程等待门闩，个数为 0 后向后执行</span></span><br></pre></td></tr></table></figure>

<p><strong>CountDownLatch 示例</strong></p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">import</span> java.util.concurrent.CountDownLatch;</span><br><span class="line"></span><br><span class="line"><span class="keyword">public</span> <span class="keyword">class</span> <span class="title class_">ThreadDemo</span> &#123;</span><br><span class="line"></span><br><span class="line">    <span class="keyword">final</span> <span class="keyword">static</span> <span class="type">CountDownLatch</span> <span class="variable">latch</span> <span class="operator">=</span> <span class="keyword">new</span> <span class="title class_">CountDownLatch</span>(<span class="number">5</span>);</span><br><span class="line"></span><br><span class="line">    <span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title function_">main</span><span class="params">(String[] args)</span> <span class="keyword">throws</span> InterruptedException &#123;</span><br><span class="line">        <span class="keyword">for</span>(<span class="type">int</span> <span class="variable">i</span> <span class="operator">=</span> <span class="number">0</span>; i &lt; <span class="number">5</span>; i++) &#123;</span><br><span class="line">            <span class="keyword">new</span> <span class="title class_">MyThread</span>().start();</span><br><span class="line">        &#125;</span><br><span class="line">        latch.await();</span><br><span class="line">        System.out.println(<span class="string">&quot;主线程继续执行&quot;</span>);</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="keyword">static</span> <span class="keyword">class</span> <span class="title class_">MyThread</span> <span class="keyword">extends</span> <span class="title class_">Thread</span> &#123;</span><br><span class="line">        <span class="meta">@Override</span></span><br><span class="line">        <span class="keyword">public</span> <span class="keyword">void</span> <span class="title function_">run</span><span class="params">()</span> &#123;</span><br><span class="line">            <span class="keyword">try</span> &#123;</span><br><span class="line">                System.out.println(getName() + <span class="string">&quot;打开门闩&quot;</span>);</span><br><span class="line">            &#125; <span class="keyword">finally</span> &#123;</span><br><span class="line">                latch.countDown();</span><br><span class="line">            &#125;</span><br><span class="line">        &#125;</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<hr>
<h2 id="CyclicBarrier-循环栅栏"><a href="#CyclicBarrier-循环栅栏" class="headerlink" title="CyclicBarrier 循环栅栏"></a>CyclicBarrier 循环栅栏</h2><p>CyclicBarrier 类也是一个同步工具类，需要进行导入：<code>import java.util.concurrent.CyclicBarrier</code>。</p>
<p>其通过 await 方法设置一个屏障，线程到达后被阻塞。只有当 N 个线程都到达屏障后才允许这些线程向后执行。和 CountDownLatch 不同，CyclicBarrier 可循环利用。常用于多线程计算数据，最后合并计算结果的场景。</p>
<p><strong>CyclicBarrier 方法</strong></p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line"><span class="type">CyclicBarrier</span> <span class="variable">barrier</span> <span class="operator">=</span> CyclicBarrier(<span class="number">10</span>); </span><br><span class="line"><span class="type">CyclicBarrier</span> <span class="variable">barrier</span> <span class="operator">=</span> CyclicBarrier(<span class="number">10</span>, ()-&gt; System.out.println(<span class="string">&quot;open&quot;</span>));</span><br><span class="line"></span><br><span class="line"><span class="comment">// CyclicBarrier 构造方法设定了参与线程的个数 N，也可以选择设定在第 N 个线程到达屏障时执行方法。</span></span><br><span class="line"></span><br><span class="line">barrier.await();                             <span class="comment">// 线程必须等到 N 个线程才能向后执行</span></span><br><span class="line">barrier.await(<span class="number">20</span>, TimeUnit.SECONDS);         <span class="comment">// 线程等待规定时间后无论如何都会向后执行</span></span><br></pre></td></tr></table></figure>

<p><strong>CyclicBarrier 示例</strong></p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">import</span> java.util.concurrent.CyclicBarrier;</span><br><span class="line"></span><br><span class="line"><span class="keyword">public</span> <span class="keyword">class</span> <span class="title class_">CyclicBarrierDemo</span> &#123;  </span><br><span class="line">    <span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title function_">main</span><span class="params">(String[] args)</span> &#123;  </span><br><span class="line">        <span class="keyword">for</span>(<span class="type">int</span> <span class="variable">i</span> <span class="operator">=</span> <span class="number">0</span>; i &lt; <span class="number">10</span>; i++) &#123;</span><br><span class="line">            <span class="keyword">new</span> <span class="title class_">MyThread</span>().start();</span><br><span class="line">        &#125;</span><br><span class="line">    &#125; </span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="keyword">class</span> <span class="title class_">MyThread</span> <span class="keyword">extends</span> <span class="title class_">Thread</span> &#123;</span><br><span class="line">    <span class="keyword">static</span> <span class="type">CyclicBarrier</span> <span class="variable">barrier</span> <span class="operator">=</span> <span class="keyword">new</span> <span class="title class_">CyclicBarrier</span>(<span class="number">5</span>, <span class="keyword">new</span> <span class="title class_">Runnable</span>() &#123;</span><br><span class="line">        <span class="meta">@Override</span></span><br><span class="line">        <span class="keyword">public</span> <span class="keyword">void</span> <span class="title function_">run</span><span class="params">()</span> &#123;</span><br><span class="line">            System.out.println(<span class="string">&quot;栅栏开启&quot;</span>);</span><br><span class="line">        &#125;</span><br><span class="line">    &#125;);</span><br><span class="line">        </span><br><span class="line">    <span class="meta">@Override</span></span><br><span class="line">    <span class="keyword">public</span> <span class="keyword">void</span> <span class="title function_">run</span><span class="params">()</span> &#123;</span><br><span class="line">        <span class="keyword">try</span> &#123;</span><br><span class="line">            Thread.sleep(<span class="number">1000</span>);</span><br><span class="line">            System.out.println(getName() + <span class="string">&quot; 到达栅栏&quot;</span>);</span><br><span class="line">            barrier.await();</span><br><span class="line">            System.out.println(getName() + <span class="string">&quot; 冲破栅栏&quot;</span>);</span><br><span class="line">        &#125; <span class="keyword">catch</span> (Exception e) &#123;</span><br><span class="line">            e.printStackTrace();</span><br><span class="line">        &#125;</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

 
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<script src="/dist/main.js"></script>

<!-- ImageViewer -->
 <!-- Root element of PhotoSwipe. Must have class pswp. -->
<div class="pswp" tabindex="-1" role="dialog" aria-hidden="true">

    <!-- Background of PhotoSwipe. 
         It's a separate element as animating opacity is faster than rgba(). -->
    <div class="pswp__bg"></div>

    <!-- Slides wrapper with overflow:hidden. -->
    <div class="pswp__scroll-wrap">

        <!-- Container that holds slides. 
            PhotoSwipe keeps only 3 of them in the DOM to save memory.
            Don't modify these 3 pswp__item elements, data is added later on. -->
        <div class="pswp__container">
            <div class="pswp__item"></div>
            <div class="pswp__item"></div>
            <div class="pswp__item"></div>
        </div>

        <!-- Default (PhotoSwipeUI_Default) interface on top of sliding area. Can be changed. -->
        <div class="pswp__ui pswp__ui--hidden">

            <div class="pswp__top-bar">

                <!--  Controls are self-explanatory. Order can be changed. -->

                <div class="pswp__counter"></div>

                <button class="pswp__button pswp__button--close" title="Close (Esc)"></button>

                <button class="pswp__button pswp__button--share" style="display:none" title="Share"></button>

                <button class="pswp__button pswp__button--fs" title="Toggle fullscreen"></button>

                <button class="pswp__button pswp__button--zoom" title="Zoom in/out"></button>

                <!-- Preloader demo http://codepen.io/dimsemenov/pen/yyBWoR -->
                <!-- element will get class pswp__preloader--active when preloader is running -->
                <div class="pswp__preloader">
                    <div class="pswp__preloader__icn">
                        <div class="pswp__preloader__cut">
                            <div class="pswp__preloader__donut"></div>
                        </div>
                    </div>
                </div>
            </div>

            <div class="pswp__share-modal pswp__share-modal--hidden pswp__single-tap">
                <div class="pswp__share-tooltip"></div>
            </div>

            <button class="pswp__button pswp__button--arrow--left" title="Previous (arrow left)">
            </button>

            <button class="pswp__button pswp__button--arrow--right" title="Next (arrow right)">
            </button>

            <div class="pswp__caption">
                <div class="pswp__caption__center"></div>
            </div>

        </div>

    </div>

</div>

<link rel="stylesheet" href="https://cdn.staticfile.org/photoswipe/4.1.3/photoswipe.min.css">
<link rel="stylesheet" href="https://cdn.staticfile.org/photoswipe/4.1.3/default-skin/default-skin.min.css">
<script src="https://cdn.staticfile.org/photoswipe/4.1.3/photoswipe.min.js"></script>
<script src="https://cdn.staticfile.org/photoswipe/4.1.3/photoswipe-ui-default.min.js"></script>

<script>
    function viewer_init() {
        let pswpElement = document.querySelectorAll('.pswp')[0];
        let $imgArr = document.querySelectorAll(('.article-entry img:not(.reward-img)'))

        $imgArr.forEach(($em, i) => {
            $em.onclick = () => {
                // slider展开状态
                // todo: 这样不好，后面改成状态
                if (document.querySelector('.left-col.show')) return
                let items = []
                $imgArr.forEach(($em2, i2) => {
                    let img = $em2.getAttribute('data-idx', i2)
                    let src = $em2.getAttribute('data-target') || $em2.getAttribute('src')
                    let title = $em2.getAttribute('alt')
                    // 获得原图尺寸
                    const image = new Image()
                    image.src = src
                    items.push({
                        src: src,
                        w: image.width || $em2.width,
                        h: image.height || $em2.height,
                        title: title
                    })
                })
                var gallery = new PhotoSwipe(pswpElement, PhotoSwipeUI_Default, items, {
                    index: parseInt(i)
                });
                gallery.init()
            }
        })
    }
    viewer_init()
</script> 
<!-- MathJax -->

<!-- Katex -->

<!-- busuanzi  -->
 
<script src="/js/busuanzi-2.3.pure.min.js"></script>
 
<!-- ClickLove -->

<!-- ClickBoom1 -->

<script src="https://cdn.staticfile.org/animejs/3.2.1/anime.min.js"></script>

<script src="/js/clickBoom1.js"></script>
 
<!-- ClickBoom2 -->

<!-- CodeCopy -->
 
<link rel="stylesheet" href="/css/clipboard.css">
 <script src="https://cdn.staticfile.org/clipboard.js/2.0.10/clipboard.min.js"></script>
<script>
  function wait(callback, seconds) {
    var timelag = null;
    timelag = window.setTimeout(callback, seconds);
  }
  !function (e, t, a) {
    var initCopyCode = function(){
      var copyHtml = '';
      copyHtml += '<button class="btn-copy" data-clipboard-snippet="">';
      copyHtml += '<i class="ri-file-copy-2-line"></i><span>COPY</span>';
      copyHtml += '</button>';
      $(".highlight .code pre").before(copyHtml);
      $(".article pre code").before(copyHtml);
      var clipboard = new ClipboardJS('.btn-copy', {
        target: function(trigger) {
          return trigger.nextElementSibling;
        }
      });
      clipboard.on('success', function(e) {
        let $btn = $(e.trigger);
        $btn.addClass('copied');
        let $icon = $($btn.find('i'));
        $icon.removeClass('ri-file-copy-2-line');
        $icon.addClass('ri-checkbox-circle-line');
        let $span = $($btn.find('span'));
        $span[0].innerText = 'COPIED';
        
        wait(function () { // 等待两秒钟后恢复
          $icon.removeClass('ri-checkbox-circle-line');
          $icon.addClass('ri-file-copy-2-line');
          $span[0].innerText = 'COPY';
        }, 2000);
      });
      clipboard.on('error', function(e) {
        e.clearSelection();
        let $btn = $(e.trigger);
        $btn.addClass('copy-failed');
        let $icon = $($btn.find('i'));
        $icon.removeClass('ri-file-copy-2-line');
        $icon.addClass('ri-time-line');
        let $span = $($btn.find('span'));
        $span[0].innerText = 'COPY FAILED';
        
        wait(function () { // 等待两秒钟后恢复
          $icon.removeClass('ri-time-line');
          $icon.addClass('ri-file-copy-2-line');
          $span[0].innerText = 'COPY';
        }, 2000);
      });
    }
    initCopyCode();
  }(window, document);
</script>
 
<!-- CanvasBackground -->
 
<script src="/js/dz.js"></script>
 
<script>
  if (window.mermaid) {
    mermaid.initialize({ theme: "forest" });
  }
</script>


    
    

  </div>
</body>

</html>